The present invention relates to a method of forming through holes in printed wiring board substrates; and more particularly to the formulation of micro through holes in the same accurately and effectively by means of a chemical etchant process.
Conventional methods of forming through holes in printed wiring boards heretofore employed include mechanical drilling, laser drilling and plasma etching among others.
Regarding mechanical drilling, it is very difficult to form micro through holes of 100 microns or less due to the difficulty in producing drills of that size that do not readily break. Also, even using a drill size of 250 microns it takes 5-6 hours to drill 10,000 holes an inordinate amount of time. Further, mechanical drilling created burrs, dust and debris that often block the holes or adhere to the surface of the substrate material requiring additional cleaning processes. Drilling apparatus required is very expensive and additional expendables like entry and back-up boards also add to cost.
Laser drilling and plasma drilling processes are incapable of forming holes in substrate materials containing glass fibers which disallows use of the most widely used and inexpensive substrates which normally do contain glass fibers. In addition, equipment to perform laser or plasma drilling is also very costly.